In the field of lithographic printing, ink is continuously conveyed from an ink source through a series of rollers to a printing plate on a plate cylinder in a printing press. Image portions of the printing plate accept ink from one or more of the last of a series of inking rollers and transfer a portion of that ink to a blanket cylinder as a reverse image from which a portion of the ink is transferred to form a correct-reading image on paper or other materials. It is also important in conventional lithographic printing processes that a dampening solution containing water and proprietary additives be conveyed continuously to the printing plate whereby transferring in part to the non-image areas of the printing plate the water functions to keep those non-image areas free of ink. Finally, in conventional printing press systems, the ink is continuously made available in varying amounts determined by cross-press column input control adjustments to a plurality of ink metering devices, such as ink injectors. Open fountain inker systems, and other systems, may also be used as ink metering devices.
Lithographic printing plate surfaces in the absence of imaging materials have minute interstices and a hydrophilic or water-loving property to enhance retention of water that is the dampening solution, rather than ink on the surface of the plate. Imaging the plate fills these interstices and creates oleophilic or ink-loving areas according to the image that is to be printed. Consequently, when both ink and dampening solution are presented to an imaged plate in appropriate amounts, only the ink tending to reside in non-image areas becomes disbonded from the plate. In general, this action accounts for the continuous ink and dampening solution differentiation on the printing plate surface, which is integral to the lithographic printing process.
During a make-ready or set up process, a printing press is prepared for a new print job. In this regard, a new print job refers to printing different images on the web as compared to an existing print job. This can be accomplished, for example, by changing the printing plate(s) on a printing unit, or by bringing a different set of printing units into contact with the web. Both require make-ready, although in the latter case, sometimes referred to as auto-transfer, the make-ready for the new print job could be performed at any time prior to the job change. In any event, during this make-ready (or set up) process, the press is adjusted and stabilized before it is ready to produce an accurate and acceptable image on the printed material. For example, adjustments are made to the press color and/or registration during start up. Thereafter, the press is run for a period of time needed for the effect of the adjustments to propagate through to the printed substrate, often referred to as the run-in time. During the run in time, the images on the printed substrate are not usable, and are often referred to as “waste.” The press may need to be stopped and started a number of times as make-ready adjustments are iteratively made until acceptable print quality is achieved.
One aspect of the make-ready process is ink stabilization. In this regard, during the run-in period noted above, it is generally necessary to operate the press, applying ink and water to the printing plate and transfer the image from the plate to the blanket in order to stabilize the ink transfer process so that the desired ink thickness, typically measured by optical density, is achieved.
Conventionally, inkers and inking rollers are geared to or linked to blanket cylinder, impression cylinder or plate cylinder so the inkers or inking rollers are not controlled independently. As a result the inkers or ink rollers may not be controlled in a manner that optimizes or maintains desired ink film thickness established in the ink roller train. In order to ameliorate this, shorter ink trains and inker forcing functions have been utilized.
It is necessary to control the correct amount of ink supplied from each of the ink injectors during lithographic printing. U.S. Pat. No. 5,027,706, the entire disclosure of which is hereby incorporated by reference, describes an inking system including controls for controlling supply of ink from an ink rail to a plurality of individual ink outlet orifices corresponding to ink columns or zones.
U.S. Pat. No. 5,179,978, the entire disclosure of which is hereby incorporated by reference, describes a rotary ink valve assembly for controlling ink or printing fluid input in a printing press.
U.S. Pat. No. 5,235,913 purports to describe a device and method for stabilizing an offset lithographic printing press. A litho start-off device comprises an ink removal cylinder which can be selectively engaged and disengaged with a blanket disposed on the surface of the blanket cylinder. When engaged with the blanket cylinder, the ink removal cylinder removes ink from the blanket of the blanket cylinder. A scraper assembly is also provided to remove the ink from the ink removal cylinder as it rotates.
U.S. 2006/0162597, the entire disclosure of which is hereby incorporated by reference, describes an integrated ink rail assembly which includes a plurality of page packs, each page pack including a corresponding ink outlet orifice corresponding to an ink column or zone.